In the process of drilling oil and gas wells, it is common to want to steer the drillbit to get the well to a desired location that is likely to have hydrocarbons trapped. While many technologies have been developed to steer the drillbit, there are many forces that resist or prevent steering. For example, when it is desired to sidetrack from an existing wellbore at some distance from the bottom of the existing wellbore, the least resistant path for the drillbit to follow is along the existing wellbore. It is a challenge to get a drillbit to bite into the side of an existing wellbore without something to push against.
To overcome the tendency of drillbits to follow existing wellbores, the conventional technique is to create a cement plug in the location where it is desired to side track out from the existing wellbore. However, the cement plug closes the existing wellbore and further production in the original wellbore below the location of the sidetrack well is blocked.
Other efforts to provide some resistance to use for creating a sidetrack wellbore include inserting an aluminum plug. The aluminum plug is more easily installed or at least less time consuming than a cement plug, but the aluminum plug tends to be kind of sloppy in the wellbore in that when the side track goes down from a somewhat horizontal well, the plug is likely to fall down into the hole when the drill string is pulled out of the side track and therefore block the side track.
Also, it should be recognized that the relative density or resistance of the formation to drilling is likely to be different than the density or resistance to the drillbit of either the cement or aluminum plug. As such, there is still some concern about the drillbit getting out of the original wellbore and being able to drill to the target formation without having too much curvature or “dogleg”. For example, it might be attractive to use a drill motor having an aggressive angle to make sure that the drillbit fully exits the existing wellbore before the end of the plug is reached. However, the aggressive angle may be less preferred if the target formation is a considerable distance from the original wellbore. A wellbore that snakes and twists too much will create too much friction when liner or casing is inserted into the side track wellbore. So, the sidetrack might be created initially with a higher angle motor, recognizing that the most severe angles for well drilling are very small (less than four degrees off center, for example) but replaced with a motor that has a much smaller angle that will reach the target with a straighter wellbore. This strategy requires two “trips” where the drillstring is withdrawn from the wellbore and re-inserted. Trips are noteworthy from a financial standpoint as it sometimes takes quite a bit of time to pull out thousands of feet of a drillstring and then re-insert the drillstring to the same point and time is money on a drilling rig.